1. Field of the Invention
The present invention relates to an electric motor, and more particularly to a small-sized linear motor employed in a portable electronic device.
2. Description of the Related Art
Electric motors convert input electrical energy to mechanical energy, based on Fleming's law that a force applied to move a conductor through a magnetic field will cause a current to flow through the conductor.
Electric motors are applied to various fields according to their size and purpose, and are widely used as vibration motors in portable terminals. Vibration motors of portable terminals have been used to inform the user of reception of a call or reception of a text message.
In recent years, due to development of technologies, portable terminals including a touch screen as an input interface are being distributed, and various user interfaces for portable terminals including a touch screen are being developed. Specifically, various methods for informing the user of the operation of a touch screen are being developed. As an example, vibration motors of portable terminals are activated in correspondence to a user's touching of a touch screen, in order to provide feedback to the user of operation of the touch screen.
In general, coin type motors or bar type motors are employed in portable terminals for traditional purposes of vibration motors such as informing the user of call or text message reception of a. However, coin type and bar type motors do not provide quick response characteristics, and output undesirable residual vibrations. Therefore, when coin type or bar type motors are used to inform the user of the operation of a touch screen, the response speed to a touch of the touch screen by the user is not quick, thus making it difficult to quickly cope with the operation of the user.
To address the above-described problem, linear motors that have a response time that is shorter than that of coin type or bar type motors, that consume less power and that have a high reliability are being employed. Linear motors are driven based on forced harmonic vibration. However, linear motors apply only one resonance frequency when vibrating, and their vibration forces rapidly decrease for frequencies other than the resonance frequency.
Moreover, due to the above-described problem, linear motors are limited in the number of various signals that can be output to inform the user of a touch screen operation. In particular, since users prefer to receive feedback at various frequencies according to individual taste and particular operation, the present invention has been developed to satisfy such user demand.